1. Field of the Invention
The present invention relates generally to space transformers for being used in probe cards and more particularly, to a space transformer using a carrier substrate which is originally made for a chip package and provided with elongated contacts, and to a method for manufacturing the space transformer.
2. Description of the Related Art
A probe card usually comprises a main circuit board adapted to be electrically connected with signal-transmitting contacts of a testing apparatus directly, and a space transformer (hereinafter referred to as “ST”) mounted to a bottom surface of the main circuit board. The space transformer is provided at a top surface thereof with a plurality of top contact pads adapted for being electrically connected with the main circuit board, and at a bottom surface thereof with a plurality of bottom contact pads adapted for being connected with a plurality of probe needles, such as vertical probe needles, respectively. The space transformer is designed in such a way that the bottom contact pads of the space transformer are arranged having an interval smaller than the interval of the top contact pads of the space transformer, so that the probe needles, which are connected with the bottom contact pads, will be also arranged with a relatively smaller interval and thereby capable of probing contact pads of a chip having a very small interval too.
For general vertical probe cards, the bottom contact pads of the space transformer are arranged conforming in position to the contact pads of the chip under test, so that the probe needles, which are connected with the bottom contact pads, will also conform in position to the contact pads of the chip under test. For lowering the manufacturing cost of the space transformer and avoiding positional deviations of the bottom contact pads of the space transformer, many commercially available probe cards use carrier substrates originally made for chip packages to serve as the space transformers. The carrier substrate, which is provided by a chip manufacturing or designing dealer to a probe card manufacturer, has an original usage of connecting a chip to a circuit board. This means the carrier substrate is originally configured with contacts corresponding in pattern to the contact pads of the chip, such that the chip can be directly and electrically bonded on the carrier substrate in a chip package. Therefore, the pattern of the contacts of the carrier substrate doesn't need to be reformed or rearranged if the carrier substrate, which is originally used in a chip package, is directly applied in the probe card for testing the chips having contact pad pattern corresponding to the contact pattern of the carrier substrate to serve as the space transformer of the probe card.
When applying the carrier substrate made for the chip package to the probe card, the probe card manufacturer mounts additional circular contact pads on the original contacts of the carrier substrate. The additional circular contact pads have relatively larger thickness and area so that the space transformer made of the carrier substrate has the reinforced contact pads with high structural strength for being contacted by the probe needles. In this way, the contact pads of the space transformer are less damageable by reacting force from the chip probed by the probe needles.
For applications in high-grade electronic devices, the chip package is developed smaller and smaller. If the carrier substrate made with reduced size for a small chip package has circular contacts with correspondingly reduced size, the circular contacts might be too small to be connected with the chip firmly. Therefore, the commercially available carrier substrates with relatively smaller size are usually provided with elongated contacts. Although the elongated contact of the small-sized carrier substrate is also very narrow, it is long enough to have sufficient area for being connected with the chip firmly.
However, the carrier substrate made for the chip package with elongated contacts is difficult to be made as the space transformer of the probe card by the conventional way of mounting large-sized circular contact pads to the original elongated contacts of the carrier substrate due to limit of the very small interval between the adjacent elongated contacts. That is, the adjacent elongated contacts will be short-circuited by the large-sized circular contact pads unless the area of each circular contact pad is reduced; however, the circular contact pads with reduced area will have insufficient structural strength.